Is "equivalent lateral load analysis" to simulate the response of a structure to ground motion
acceptable? Absolutely NOT when an Eigen solution shows that no single mode contributes a large
enough modal mass participation (say around 90%) that it can be justified to be the mode that
predominates the response of a structure to ground motion.

This is often the case for a variety of industrial structures where a large number of modes are required to achieve an acceptable value of total dynamic mass participation (>=90%) in connection with seismic analysis and where each mode makes a relatively small contribution to the total mass participation. For these cases, ONLY a rigorous Response Spectrum analysis is acceptable.

Did you know that GT STRUDL was used to analyze the 40 foot high Chick-Fil-A Cow in Atlanta?